Insulating glass units (also known as insulating glazing units or “IGUs” or “IGs”) and vacuum insulating glass units (also known as vacuum insulating glazing units or “VIGUs” or “VIGs”) are known. They comprise two or more parallel but spaced-apart sheets, or panes, of glass attached and/or sealed to one another around their respective peripheries. The gap between each pair of sheets or panes of glass (also known as “lites”) defines a cavity. In IGUs, the cavity is filled with air or other gasses such as argon, krypton or xenon, whereas in VIGUs, the gap is “filled” with or contains a reduced-pressure atmosphere or a vacuum. Spacers (also known as “stand-offs” or “suspenders”) are typically disposed within the gap of IGUs and VIGUs to maintain the gap. In the case of VIGUs, spacers are particularly necessary in order to support the sheets of glass against the pressure of the outside air, which otherwise might distort or damage the glass, or cause the two panes of glass to come in contact with each other so as to produce a thermal “short circuit” (i.e., a thermally conductive path directly through the panes of glass).
Using vacuum to increase the insulating performance of window glazing components is not a new concept, and in fact many innovative approaches have been taught in the literature over the last 75 years. It is, however, readily observed by skilled practitioners of the art that the majority of the prior work relates to low-to medium-vacuum levels, i.e., vacuum levels within the range from about 760 torr (1 atmosphere of pressure at sea level) to about 10−3 torr. Note, for purposes of this application, a “higher” level of vacuum is understood to correspond to a lower absolute pressure, e.g., a vacuum level of 10−4 torr is a higher vacuum than 10−3 torr. In a few cases the literature makes reference to the measured vacuum levels in glazing components, but in many cases the maintainable vacuum level must be interpreted from careful evaluation of the materials exposed to the vacuum enclosure, the methods used to create the vacuum seal and the methods used to produce the vacuum condition in the enclosed space.
While the literature describing vacuum insulating window glazing components may not rigorously define the vacuum levels, literature from other industries, such as the electronics industry, defines different vacuum levels and the types of materials and processing methods required to achieve and maintain those specified vacuum levels. The common distinction between medium- and high-vacuum devices is a vacuum level of 10−3 torr. In other words, the range of high-vacuum levels begins at about 10−3 torr and goes higher, i.e., in the direction toward and/or past 10−4 torr. In the case of vacuum insulating glass units (“VIGUs” or “VIGs”) for windows, doors and other components, where it is desirable for the VIGs to retain a prescribed minimum vacuum level for an extended operating lifetime (e.g., 25 years), a vacuum containment system capable of initially maintaining a higher level of vacuum (e.g., 10−4 torr to 10−5 torr), may be necessary.
One purpose of high vacuum insulating glass units (“HVIGUs”) is to provide lower levels of conductive heat losses between temperature-controlled spaces and non-temperature-controlled spaces, or between different temperature-controlled spaces, that are separated by this glazing unit (i.e., compared to VIGUs with low or medium-vacuum levels). In such cases, providing this desired lower level of conductive heat transfer over a long period of time is desirable. Since the ambient conditions in the uncontrolled space, most commonly the external atmospheric environment, produce a variety of stresses including thermal, pressure and mechanical vibration, and since, to a lesser extent, this also happens in the conditioned space, various embodiments of the HVIGU will be more or less capable of surviving the applied stresses while maintaining the desired minimum vacuum level. Thus, the design lifetime, i.e., the period of time that the HVIGU will maintain its desired level of performance, is one of the performance features of the HVIGU.
VIGUs and HVIGUs have multiple applications in addition to their use as the glass unit (component) of windows for residential and non-residential buildings. Examples of other (non-fenestration) uses include glass windows for refrigerated supermarket display cases (supermarket refrigerators and freezers); thermally-insulating covers for active and/or passive solar collectors; windows for transportation vehicles including spacecraft, aircraft, automobiles, trains, buses and watercraft (boats, ships and submarines); and many other applications.
As previously described, IGUs, VIGUs and HVIGUs are typically constructed using at least two spaced-apart sheets or panes of glass, each of some prescribed thickness. The gap between two adjacent glass sheets or panes defines a cavity. In IGUs, the cavity is filled with air or other gasses such as argon, krypton or xenon, whereas in VIGUs and HVIGUs, the gap is “filled” with a reduced pressure atmosphere or a vacuum. Spacers (also known as “stand-offs” or “pillars”) are typically disposed within the gap of IGUs, VIGUs and HVIGUs to maintain the gap. In the case of VIGUs and HVIGUs, spacers are particularly necessary in order to support the sheets against the pressure of the outside air, which otherwise might distort or damage the glass, or cause the two panes of glass to come in contact with each other so as to produce a thermal “short circuit.”
These glass panes are then sealed, typically along the edges, using some arrangement of sealing elements which are intended to isolate the evacuated volume from the surrounding atmospheric pressure. Since the primary objective of the VIGU or HVIGU is to provide a low thermally-conductive barrier between environmental spaces, each of which may have a higher or lower temperature with respect to the other, it is obvious to skilled practitioners of the art that the two panes of glass may reach temperature levels which vary distinctly from each other. In fact, for a given space-to-space temperature differential, the pane-to-pane temperature differential will typically increase as a function of reduced thermal conductivity of the VIGU or HVIGU. As a result of the temperature differential between the panes of glass, the panes may expand and contract differentially. This may also introduce differential movement of the spacers relative to one or both panes of glass.
For reference purposes, in a dual pane IGU, VIGU or HVIGU, the outdoor-facing or outside-facing glass pane of an IGU/VIGU/HVIGU is typically referred to as glass lite #1, and the indoor-facing or inside-facing glass pane is typically referred to as glass lite #2. There are typically four glass surfaces of interest, denoted (in order from outside to inside) as surfaces 1, 2, 3 and 4. Surfaces 1 and 2 are, respectively, the outdoor facing and indoor facing surfaces of glass lite #1, and surfaces 3 and 4 are, respectively, the outdoor facing and indoor facing surfaces of glass lite #2. Thus, surfaces 2 and 3 are typically disposed on opposite sides of the cavity of the IGU/VIGU/HVIGU.
Similarly, in a triple pane IGU, VIGU or HVIGU, the outdoor-facing or outside-facing glass pane of an IGU/VIGU/HVIGU is typically referred to as glass lite #1, the middle glass pane is referred to as glass lite #2 and the indoor-facing or inside-facing glass pane is typically referred to as glass lite #3. There are typically six glass surfaces of interest, denoted (in order from outside to inside) as surfaces 1, 2, 3, 4, 5 and 6. Surfaces 1 and 2 are, respectively, the outdoor facing and indoor facing surfaces of glass lite #1, surfaces 3 and 4 are, respectively, the outdoor facing and indoor facing surfaces of glass lite #2 and surfaces 5 and 6 are, respectively, the outdoor facing and indoor facing surfaces of glass lite #3. Thus, surfaces 1 and 6 are typically disposed on opposite outer surfaces of the overall IGU/VIGU/HVIGU, surfaces 2 and 3 are typically disposed facing one another on opposite sides of the outer cavity between lites #1 and #2 and surfaces 4 and 5 are typically disposed facing one another on opposite sides of the inner cavity between lites #2 and #3 of the IGU/VIGU/HVIGU.
Vacuum insulated glass units (VIGUs/HVIGUs) are of interest for window applications because of their extremely high insulating properties, with center-of-glass insulating or thermal resistance R values as high as R-13 or more, expressed in US units of British Thermal Units as ft2·° F.·hr/Btu. (conductive U-Values or U-Factors of 0.07 or lower, expressed in US units of BTU/(h·° F.·ft2)).
The conversion between SI and US units of R-value is 1 h·ft2·° F./Btu=0.176110 K·m2/W, or 1 K·m2/W=5.678263 h·ft2·° F./Btu.
Creating the reduced pressure between two or more lites surrounded by a metal band hermetically bonded to the perimeter of the two lites in a two-lite VIGU or HVIGU or to three or more lites of a VIGU or HVIGU with three or more glass lites can be very difficult. Evacuation of the VIGU/HVIGU's cavity or cavities often requires evacuation times of eight hours or more when a small vacuum septum fabricated into one or more of the VIGU/HVIGU's lites is used as the evacuation port. When vacuum septums fabricated into one or more lites are used, they are usually covered and protected from damage after the evacuation process by attaching with an adhesive or epoxy a cover over the then hermetically-sealed septum. The cover is typically a stainless-steel disk.
The use of a gettering material (also know as “getter material” or “getters”) is well known to those skilled in the art of hermetic packaging. Getters are designed and made of materials to have an affinity to one or more non-noble gases to have the gas or gases stick or be absorbed by the getter upon impact with the getter rather than continue to remain moving in the package's atmosphere. In some cases the atmosphere inside the package may be a partial pressure atmosphere, e.g. a vacuum.